fix: refresh occluded browser windows before plugin capture

tests/capture-fixture.ps1

@@ -1,9 +1,9 @@
-param([string]$Title, [string]$ReadyFile, [switch]$Cover)
+param([string]$Title, [string]$ReadyFile, [switch]$Cover, [int]$Width=500, [int]$Height=300)
 Add-Type -AssemblyName System.Windows.Forms
 Add-Type -AssemblyName System.Drawing
 $form = New-Object System.Windows.Forms.Form
 $form.Text = $Title
-$form.Size = New-Object System.Drawing.Size(500, 300)
+$form.Size = New-Object System.Drawing.Size($Width, $Height)
 $form.StartPosition = 'Manual'
 $form.Location = New-Object System.Drawing.Point(100, 100)
 $form.TopMost = $true